1. Field of the Invention
The present invention relates to an outboard engine assembly for use on small boats which has in its upper region an internal combustion engine having a substantially vertical crankshaft and a vertical array of cylinders each extending substantially horizontally, and an internal combustion engine for use in such an outboard engine assembly.
2. Description of the Prior Art
Some outboard engine assemblies are mounted on the stern of a boat by an attachment including a stern bracket, a swivel case, a swivel shaft, etc., and include an engine supported by rearwardly extending upper and lower support arms disposed above and below, respectively, the attachment. The engine has a substantially vertical crankshaft and a vertical array of cylinders each having an axis extending substantially horizontally. The engine is disposed in an upper region of the outboard engine assembly by the upper support arm.
Increasing the engine displacement and the number of cylinders of such an outboard engine assembly for a higher engine output power results in an increase in the vertical dimension of the engine, i.e., in the vertical dimension of the outboard engine assembly above the upper support arm.
The outboard engine assembly is usually tiltable about a horizontal tilt axis in the attachment. If the vertical dimension of the outboard engine assembly above the upper support arm is increased, then when the outboard engine assembly is tilted upwardly at the time the boat is anchored or placed ashore, it projects greatly into the boat.
For reducing the size and weight of an outboard engine assembly, it has been proposed to couple the upper support arm to opposite sides of the engine as disclosed in Japanese laid-open patent publication No. 59-176192.
Japanese laid-open patent publication No. 63-192693 also shows an outboard engine assembly with an engine supported in an upper region by an upper support arm that is joined to opposite sides of the engine. The engine has a substantially vertical crankshaft whose lower end is connected to a vertical shaft for transmitting rotational power from the engine to a propeller shaft.
However, the lateral dimension or width of the above disclosed outboard engine assemblies is increased because the upper support arm is coupled to the opposite sides of the engine.
The engine of the outboard engine assembly disclosed in the latter publication has a balancer mechanism for attenuating engine vibrations, the balancer mechanism having balancer shafts parallel to the crankshaft of the engine. The balancer mechanism is positioned in an upper portion of the engine. The balancer mechanism thus positioned necessarily raises the center of gravity of the engine. Care should be exercised in the design of the outboard engine assembly to keep the balancer mechanism out of physical interference with various engine accessories including a carburetor, a starter motor, a flywheel, etc., and also with an engine support structure.
Another known outboard engine assembly with a substantially vertical crankshaft has a vertical array of two horizontal cylinders in its upper region and a single carburetor for supplying atomized fuel into combustion chambers in the cylinders. If the engine displacement is increased and three or more cylinders are used for a higher engine output power, then as many carburetors as the number of cylinders are required to be installed in a vertical array. The vertical array of three or more carburetors on one side of the engine cylinders puts a limitation on the space available around the engine, and necessitates a complex engine maintenance procedure.